Preparing viscose rayon



United States Patent PREPARING VISCOSE RAYON Byron A. Thumm, Swarthmore, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Application April 23, 1956 Serial No. 579,768

4 Claims. Cl. 106-165) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers ofregenerated celluv lose' from viscose.

I solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfie. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscoseof the desired cellulose and alkali content. After filtration, the viscose solution is allowed 'to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments,

the viscosesolution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous'acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqeous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purifiaction, bleaching, possibly other treating operations and drying, being collected either before or after these treatmen The filaments as formed by the conventional methods,

' consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these dilferent portions possess diiferent swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subjected to fibrillation and is relatively stiff. Ithasnow been discoved that the presence of small amounts of alkali-soluble reaction products of N,N-2 ethyl-butyramido ethylene diamine with an alkylene oxide in viscose results in the production of shaped bodies of regenerated'cellulose such as filaments, films,

sheets and the like composed of all. skin and having im proved properties and characteristics providing that the amount of the ester is maintained with certain limits and the composition of the spinning bath is maintained within certain composition limits whichwill be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of such compounds which may also be termed alkylene oxide adducts .of N,N'-2 ethyl butyramido ethylene diamine wherein the amino hydrogen atoms have been replaced with hydroxyoxyalkylene radicals or hydroxypolyoxyalkylene radicals derived from such alkylene oxides as ethylene,

propylene and butylene oxides. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic solution, the

. and may vary up to about 5 alkylene oxide such as butyramido ethylene diamine.

ethylene oxide units per molecule of N,N-2 ethyl The production of all skin products requires that certain minimum amounts of the adduct be in solution in the viscose.- The adduct may be conveniently added to viscose in the form of a solution in alkali or in water.

The amount of the adduct or reaction product which is incorporated in the viscose must be at least about 0.3% by weight of the cellulose and mayv vary up to about 3%, preferably, the amount varies from about 0.5% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined Wood pulp for the manufacture of viscose, before or during shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 4% to about 10% cellulose, the particular source of the cellulose 3 salt point designate the conventional sodium chloride salt test.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the esters in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consiting of filaments composed entirely of skin.

Genericallyand in terms of the industrial art,'the spin ning'bathis a low acid-high zinc spinning bath. The bath should contain fromabout to about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from '4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may varyfrom about 25 C. to about 80 C., preferably'between about 45 C. to about 70 C. In the production of the all 'skintype filaments, the temper'ature of the spinning bath is not critical, however, as

is well known in the conventional practice in the art, certain-of the physical properties such as tensile strength varydirectly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with'the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the'desired high tensile'stre'ngth.

' The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. The slubbing point for any specific viscose solution is in accord with usual practice determined by visual observation. For commercial operations, the acid concentration is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the concentration at which the neutralization of the caustic of the viscose is sufliciently rapid to form a filament having a skin and core. This maximum acid concentration may be determined by visual observation of the filaments. Thus, the permissible acid content of the bath may be regulated solely by visual observation without analysing the bath to determine the amount of acid present.

There isa maximum acid concentration for any specific viscose composition beyond which the neutralization is sufficiently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the commercial production of the all skin products from a 7% cellulose, 6% caustic viscose containing the adduct lies between about 5% and about 8.5%. The acid concentration may be increased as the amount of adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of adduct and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid content of the bath is increased above the maximum value although the amount of added adduct is increased beyond about 3% while other conditions are maintained constant. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 36% (based on the weight of the cellulose) carbon disulfide and 1% (based on'the weight of the cellulose) of an adduct as described hereinabove containing 2 ethylene oxide units per molecule and having a salt test of 9 to 9.5 when xtrude'd into spinning baths containing 16% to 20% sodium sulfate, 4% to 8% zinc sulfate and sulfuric acid 'notmore than about'8%, results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of acid result in the production of products having skin and core. It has been determined that the maximum permissible acid content of the bath in practicing the present invention is approximately 9%. A lowering of the amount of adduct, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissiole acid concentration for the production of all skin filaments.

The presence of the adduct in the viscose retards the coagulation and, therefore, the amount of adduct em ployed must be reduced 'at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 0.75%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufficient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes asthe fabrication of tire cord, the filaments .are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute .acidsolution and may be stretched from about 70% to about 110%, preferably between 75% and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies .such as sheets, films, tubes and'the like. The filaments tionhas notpreviously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application ofa finishing or plasticizing material and drying beforeor after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

vRegenerated cellulose filaments prepared from viscose containing the small amounts of the alkali-soluble adducts or reaction products and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface :and consist substantiallyentirely of skin. Because of the uniformity of structure throughout the filament, the .swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skinhave a high toughness and a greater flexing life which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventionalfilaments, as inzthe production of the tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. .Filaments prepared from viscose conthe filaments are not restricted to such uses and may be used for other'textile applications.

The invention may be illustrated by reference to. the preparation of regenerated cellulose filaments. from a viscose containing about 6.7% cellulose, about 5.9% caustic soda, and having a total carbon disulfide content of about 36% based on the weight of the cellulose. The viscose solutions were prepared by exanthating alkali cllulose by the introduction of 36% carbon disulfide, based on the weight of the cellulose, and churning for about 2% hours. The cellulose xanthate was then dissolved in caustic soda solution. The viscose was then allowed to ripen for about 28 hours at 18 C. In those instances where an ester was incorporated in the viscose, the desiredamount of the adduct was added to the viscose and mixed for about V2 hour before allowing the viscose to ripen. In each instance, the viscose was extruded through a spinneret to form a 100 filament yarn having a denier and at a rate set forth in the table which follows. The coagulating and regenerating bath was maintained at a temperature of about 60 C. The yarn after removal from the spinning bath was passed through a hot water bath maintained at about 95 C. and was stretched while in the hot water. The yarn was then collected in a spinning box, washed free of acids and salts and dried.

The specific spinning conditions and the physical properties of the yarns are set forth in the following table:

Example I II III IV V VI VII VIII Viscose:

Percent Adduct.-- 1 2 2 0.5 1 0.5 1 B flfalt Test 11.2 11.2 11.2 11. 2 9. 4 9. 4 9. 4 9.4

Percent H S0 8. 2 8.2 8. 2 8. 2 8.4, 8. 4 8 8 Percent ZnSO 6 6 6 6 6 6 5 Percent N a SO 16 16 16 16 15 15 15 enier 200 210 210 210 230 225 225 230 Spin Speed 22 22 22 22 36 36 36 36 Percent; Stretch 83 83 83 83 76 76 76 76 T.dr 3.2 3.5 3.4 3.5 2.9 2.7 2.7 2.7 T. wet. 2. 3 2. 7 2. 5 2. 6 1. 9 1. 6 1. 9 1. 8 dry 19 22 21 21 18 18 19 18 27 30 26 28 21 23 21 24 60 100 100 100 100 100 100 100 Norm-Adducts or reaction products in viscose of Examples II, III, V and VI, 2 ethylene oxide units/molecule N, N '2 ethyl-butyramido ethylene diamine. Examples IV, VII and VIII, 4 ethylene oxide units] molecule N, N -2 ethyl-butyramido ethylene diamine.

Spin speed-Speed of extrusion of viscose in meters per minute.

dry and T. wet- Tensile strength of dry and wet yarn, respectively, in grams per denier. tiEi dry and E. wetPercent elongation of dry and wet yarn, respecve y.

The individual filaments formed in accordance with this invention have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. 1500 The filaments of the control yarn (Example I) formed from the same viscose solution and spun under substantially identical conditions as Examples ll, III and IV but without the added adduct exhibit a very irregular and serrated surface and are composed of 60% skin and the balance core with a sharp line of demarkation between the skin and core.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tensile strength and elongation, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties disclosed hereinbefore.

.One of the properties of viscose rayon which has limited its uses is its rel'atively'high cross-sectional Swening when wet with water, this swelling amounting to from about 65% to about for rayon produced by conventional methods. Rayon filaments produced in accord ance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about If desired, small amounts of the adduct may beadded to the spinning bath. Since the adducts are water-soluble, some of the modifier 'will be leached from the filament or other shaped body and will be present in the bath.

The adducts may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adducts or reaction products may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportion of the additive at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

The term adduct is used herein synonymously with reaction products and designates the substances formed wherein the amino hydrogen atoms are replaced with at least one hydroxyalkylene radical or a hydroxypolyoxyalkylene radical, as described hereinbefore.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes andvariations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A viscose spinning solution containing a small amount of an alkali-soluble reaction product of an alkylene oxide selected from the group consisting of ethylene oxide, propylene oxide and butylene oxide with N,N'-2 ethyl-butyramido ethylene diamine, the reaction product containing from about 2 to about 5 alkylene oxide units per molecule of N,N'-2 ethyl-butyramido ethylene diamine, said small amount of the reaction product being a quantity sufiicient to impart a smooth, non-crenulated surface and a substantially all skin structure to products formed by spinning the viscose at a salt test of at least 8 into an aqueous bath containing from 10% to 25% sodium sulfate, from 3% to 15% zinc sulfate and not exceed ing 8% sulfuric acid but the quantity being insufiicient to adversely aflEect the physical properties of such products.

2. A viscose spinning solution as defined in claim 1 wherein the reaction product is an ethylene oxide reaction product.

3. A viscose spinning solution containing from about 4% -to about 10% cellulose and from .about 0.3% zto about -3% ,.-basedton the weight of the cellulose in the visccose,-.of an alkali-soluble reaction product of an alkylene oxide selectedfrom the groupconsisting ofethylene'oxide, propylene oxide iandbutylene oxide with 'N,N-2 ethylbutyramido ethylene -.diamine, the reaction product containing between about 2 and about 5 allgylene oxide units per molecule of N,N-2 ethyl-butyramido ethylene diamine.

References Cited inthe vfile of this .patent "UNITED STATES PATENTS Cox V V V Dec. 126, .1950 MacLaurin Apr. 22, 1952 'Richter Aug. 11, 1953 Charles et a1. Dec. 29, 1953 ,Drisch Mar. 29,, .1955 Tach'ikawa Jan. 24,1956 Mitchell Sept. 3, 1957 

1. A VISCOSE SPINNING SOLUTION CONTAINING A SMALL AMOUNT OF AN ALKALI-SOLUBLE REACTION PRODUCT OF AN ALKYLENE OXIDE SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDE, PROPYLENE OXIDE AND BUTYLENE OXIDE WITH N,N''-2 ETHYL-BUTYRAMIDO ETHYLENE DIAMINE, THE REACTION PRODUCT CONTAINING FROM ABOUT 2 TO ABOUT 5 ALKYLENE OXIDE UNITS PER MOLECULE OF N,N''-2 ETHYL-BUTYRAMIDO ETHYLENE DIAMINE, SAID SMALL AMOUNT OF THE REACTION PRODUCT BEING A QUANTITY SUFFICIENT TO IMPART A SMOOTH, NON-CRENULATED SURFACE AND A SUBSTANTIALLY ALL SKIN STRUCTURE TO PRODUCTS FORMED BY SPINNING THE VISCO AT A SALT TEST OF AT LEAST 8 INTO AN AQUEOUS BATH CONTAINING FROM 10% TO 25% SODIUM SULFATE, FROM 3% TO 15% ZINC SULFATE AND NOT EXCEEDING 8% SULFURIC ACID BUT THE QUANTITY BEING INSUFFICIENT TO ADVERSELY AFFECT THE PHYSICAL PROPERTIES OF SUCH PRODUCTS. 